/Engine/Source/Runtime/Engine/Public/AudioStreamingCache.h
Returns an array of the USoundwaves retaining the least recently used retained chunks in the cache. This can potentially return soundwaves for chunks that are retained by a currently playing sound, if the cache is thrashed enough.
[TArray](API\Runtime\Core\Containers\TArray)< [FObjectKey](API\Runtime\CoreUObject\UObject\FObjectKey) > GetLeastRecentlyUsedRetainedSoundWaves ( int32 NumSoundWavesToRetrieve )